Currently, the tsunami source caused by the Nankai Trough Earthquake has been announced, and the damage based on this source has been estimated and countermeasures are in progress. However, it is published that the tsunami trace of the 1498 Meio Tokai earthquake is higher than the current estimate. In order to revise countermeasures, it is important to clarify the generation and propagation of the tsunami. So I comfirmed the reproducibility using published models at first. As a result I estimated several local tsunami sources in Suruga Bay, and showed that a tsunami source of 20m to 43m is needed.

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 In the 2011 Tohoku earthquake tsunami disaster, the delay of understanding damage situation increased the human damage. To solve this problem, it is important to search the severe damaged areas. The tsunami numerical modeling is useful to estimate damages and the accuracy of simulation depends on the tsunami source.
 In this study, we proposed the new method to estimate the characterized tsunami source model by using the limited observed data of GPS buoys. The model consists of Large slip zone (LSZ), Super large slip zone (SLSZ) and background rupture zone (BZ) as the Cabinet Office, Government of Japan^{10), 11)} reported after the Tohoku tsunami.
 At the beginning of this method, the rectangular fault model is assumed based on the seismic magnitude and hypocenter reported right after an earthquake. By using the fault model, tsunami propagation is simulated numerically, and the fault model is improved after comparing the computed data with the observed data repeatedly. In the comparison, correlation coefficient and regression coefficient are used as indexes. They are calculated with the observed and the computed tsunami wave profiles. This repetition is conducted to get the two coefficients close to 1.0, which makes the precise of the fault model higher. The proposed method by using GPS buoy was applied for a tsunami scenario in the Nankai Trough. As a result, the final estimated Moment magnitude (Mw) and the location of LSZ and SLSZ are estimated well.

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 Subaerial landslides sometimes rushed into the sea and generated giant tsunamis, for example, Ariake Sea Tsunami in 1792 and Lituya Bay Tsunami in 1958. Several models have been proposed to evaluate tsunami generated by landslide but not enough knowledge has been obtained. In this study, we proposed a new practical method in which the motion of landslide was simulated by TITAN2D which is a granular flow model code for a incompressible Coulomb continuum, and the propagation of tsunami was simulated by using two-layer shallow water model. The method was verified by the simulation of 1792 Ariake Sea Tsunami caused by collapse of the eastern slope of Mayuyama. The result of the landslide simulation was approximately consistent with the measured area of deposition, and the result of the tsunami simulation was compared with tsunami trace heights and satisfied criteria of JSCE.

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 Applicability of a tsunami inundation model with the polygonally nested grid system and its MPI-parallelization to nation-wide tsunami forecast was examined in terms of accuracy and computational costs through tsunami simulation at multiple grid resolutions of 270, 90 and 30 m. The computation efficiency of the tsunami model, in which the configuration of the grid system is extended from rectangular to polygonal regions so that deployment of high-resolution grids is confined to coastal lowland, was further improved by about 14 %. This paper also proposes an automatic way of setting the polygonally nested grid system, and elucidates that it requires 140 Tflop/s supercomputer resources to complete tsunami inundation forecast for the entire coast of Japan at resolution of 30-meter grids within 10 minutes.

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 The purpose of this research is to develop STOC-CADMAS-STR system, which is numerical fluid simulator coupling with the structure analysis to efficiently calculate all stages from tsunami source to runup including the deformation of structures. We also investigated the stability of breakwaters at K port. The numerical results were compared with the physical experiments. It was good agreement with the experimental ones. Finally, the system applied to the local situation at K port to verify its applicability. The most breakwaters were washed away, whose situation was similar to the damage at K port.

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 The tsunamis ascending the rivers, were simulated numerically, using the nonlinear shallow water equations. In the present cases, the crest and trough of the incident waves, were not symmetric, rsulting in mass transport into the river, with a gradual increase in the mean water level. When the angle between a main, and a tributary, rivers is narrow, the tsunami height in the latter increased. In the cases determining the tsunami ascending the Kimotsuki River, Kagoshima, Japan, as the still water level was increased, the phase velocity of the tsunami increased. As the incident wave period was increased, the maximum water level in each wave increased, although it decreased owing to the flood channel.

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 The purpose of this study is to clarify the effect of different protective facility damage levels on tsunami inundation. We developed a method to evaluate tsunami inundation using a fragility curve that represents the relationship between tsunami height and facility damage levels. The adequate results were obtained as the results of carrying out the test calculation and the real scale calculation. In addition, because comparisons of the calculation result actually lowered the top end height of the protective facility, it was found that the result is similar to the reduction of the top end height by about 30%.

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 In this study, we developed the model for tsunami drifts analysis considering effects of structures such as buildings and tsunami barriers. The developed model can consider the interaction between tsunami drifts and tsunami propagation. The model can also be considered behavier of the tsunami drifts at a wide variety of situation and can be extended based on 2-dimensional tsunami simulation model. As the example of application, we applied for a analysis of behavior of tsunami drifts around a building to estimate the validity of developed model and applied for a variety of tsunami drifts around structures. From these results, the deloveloped model can estimate a wide variety tsunami drifts behavior by using extended tsunami simulation model.

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 Because use of vehicles during evacuation caused serious damage in Tohoku earthquake, it was recognized that it was necessary to think about ways to evacuate safely even if the residents use cars. In this research, we propose a numerical model considering the interaction between pedestrians and vehicles in evacuation. By observing the behavior of the pedestrians and vehicle in the field experiment, getting the basic data of simulation and verifying the simulation model were carried out. Then, we adapted the model into Tokushima City where is predicted severe damage by the Nankai Trough Earthquake Tsunami. Twe examine the influence of using vehicles in evacuation, 4 cases of ratio of vehicles to pedestrians were caluculated. As a result, when the amount of automobiles is over 25%, the completed evacuation rate was decreasing. Moreover, some congestion places due to mixing pedestrians and vehicles was found.

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 An integrated tsunami model consisting of models for simulating tsunami inundation, drifting objects and sediment transport, was newly developed to evaluate the effects of these multiple phenomena. A scenario of complex tsunami damage enlargement in a bay with bottleneck was revealed. The tsunami hazards in Kesennuma City, especially at the inner part of the bay such as Shishiori area, were enlarged by erosion in the bottleneck of the bay. The bathymetric change increased the drift distance of the drifting vessels. In addition, through the tsunami fragility functions based on dataset of actual damaged building and numerical results, it was evaluated that the 200 - 1,800 wooden buildings were washed away owing to sediment transport. Furthermore, it is found that the estimation accuracy of damage scale by the conventional fragility functions was suitable, although the estimated building damage near the sea and inland was under and overestimated, respectively.

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 In this study, it was found that through the numerical simulations of sediment transport in case of the 2011 Great East Japan Earthquake and Tsunami in Rikuzentakata City, the water level of the entire city area increased roughly by 1 m through the damage of the seawalls and the water level on the eastern and inner parts also increased remarkably because of the sand dune and riverbed erosion. Moreover, such damages caused the return flow near the coast line to amplify by about twice. On the other hand, using offshore tsunami waveforms, this study proposed a quantitative estimation method of the magnitude of return flow, M_RF. Estimation of the M_RF was then performed and applied for the Nankai Trough Great Earthquake and Tsunami. The return flow around Tosashimizu and Tokai Area would be equal to or greater than those on Rikuzentakata City or Onagawa Town during the 2011 tsunami. Based on lessons from the 2011 tsunami, since M_RF was larger than 0.0003, the typical value in Sanriku Coast, M_RF will be important reference for consideration among other countermeasures against future tsunamis.

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 The underestimation of 2011 Tohoku tsunami caused serious damage. Reconsideration for tsunami estimation needs knowledge of paleotsunamis. The historical records of giant tsunamis are limited, because they had occurred infequently. Tsunami deposits may include many of tsunami records and are expected to analyze paleotsunamis. However, present research on tsunami deposits are not able to estimate the tsunami source and its magnitude. This study investigated the formation mechanism of tsunami deposit by hydraulic experiment. The effect of sand grains and bore wave were examined. As the result, bore wave amplitude and multiple waves were related with the amount of deposit and distance of run-up. The mixed ratio of three grain sizes in sand bed section corresponded with the composition ratio of the sand deposit near the shoreline. Further, cutoff wall and shorter wave period increased tsunami deposits.

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 For the advancement of the tsunami load and scale evaluations, the dependency of the density of the tsunami inundation water on the hydraulic quantities, and the dependencies of the tsunami run-up distance, deposit distance, deposit thickness on the density of the tsunami inundation water are examined through a devised hydraulic experiment. Within the experimental range of this study, it is veryfied that the density of the tsunami inundation water depends on Froude number of the incident tsunami and the sediment grain size, and the relative tsunami run-up distance (=the run-up distance of the inundation water with the sediment/the run-up distance of the inundation water without the sediment), ratio of the tsunami deposit distance to the tsunami run-up distance, ratio of the mean tsunami deposit thickness to the tsunami deposit distance depend on the density of the tsunami inundation water, and then four empirical expressions for those dependencies are proposed.

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 In order to establish a method to evaluate erosion resistance and its limit of vegetation such as trees on coastal dunes, we conducted field surveys on the vertical profile of the root quantity, and hydraulic experiments on erosion of soil with roots. Erosion process in which erosion depth rapidly increased after the erosion depth exceeded the soil layer with less root density in the soil was observed also in the soil sampled in coastal dunes. A parameter on erosion resistance in an erosion calculation formula considering temporal variation of friction velocity was associated with root density in the soil.

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 For tsunami mitigation, suitable arrangement of multiple tsunami measure structures is very important. The objective of this study is to estimate effect of a combined position of coastal forest and embankment on tsunami flow pattern and fluid force acting on tree by the hydraulic model experiment.
 When the coastal embankment is in the lower stream side of the coastal forest, the fluid force acting on trees becomes large, and the coastal forest is expected as resistance to tsunami. And tsunami mitigation effect becomes most significant (i.e. runnp height becomes most smallest) when the embankment is in the lower stream side of the coastal forest.

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 Some reports for the cases such as the 2011 Tohoku Tsunami and the 2013 Typhoon Haiyan pointed out that the coastal damages expanded due to the short waves which come together with the long wave. The objective of this study is to investigate characteristics of wave force in such wavefield based on laboratory experiments. Characteristics of the wave forces measured by wave pressure sensors were examined with waveforms estimated by image analysis of video footage during the experiment. It was found that the vertical acceleration of the water motion due to short waves was one of the influential factors for the wave force. It was also found that the location change of wave breaking induced by the interaction between short and long waves maximizes the impulsive breaker force of short waves affecting the structure, and it could be dominant rather than that of the long wave.

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 Our study is aimed to propose a strategic design using numerical tsunami analysis to design a coastal forest zone. In our first-level analysis focusing on hazard reduction, we inputted our expanded coastal forest plan along with actual topography data into a numerical analysis to estimate building damage caused by a tsunami in Iwanuma City. Our estimations showed that the effect of our coastal forest expansion strategy on the coastal regions was large compared to the inland effect, and caused the reduction of building damage, particularly in the Tamaura region. In our second-level analysis focusing on the reduction of human damage, we found that increasing the amount of coastal forest within a multipronged tsunami mitigation scheme could extend the evacuation distance for the Tamaura Elementary by over 100m. The numerical analysis-based design methodology presented in this study can be used to carry out this work in regions that are likely to be exposed to tsunamis in the future.

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 On the tsunami disaster mitigation, it is important to take measure against buildings damage and disaster debris in addition to inundation. In this study, a tsunami numerical model considering building collapse and disaster debris model was applied for Owase City which is assumed to receive great damage by the Nankai Trough tsunami. And, the effect of tsunami damage evaluation which focused on the difference in the type of buildings structure in the coastal area was also studied. As a result, the proposed model predicts accurate inundation compared with the conventional model. The proposal model was able to estimate the damage of buildings and disaster debris, and also made it possible to estimate the damage by various tsunami scenarios quantitatively and concretely. The proposed model seems to be useful for the tsunami disaster prevention plan such as the damage estimation and mitigation.

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 The 2011 Great East Japan tsunami caused large scale devastated damage in both offshore and inland areas. There are many previous researches that were focusing on the relationship between tsunami characteristics and damage or loss such as human loss, building damage and fishing boat damage. Similarly, great damage and loss of aquaculture and marine ecosystem was also caused by the 2011 tsunami. However, relationship between the tsunami and their damage has not been studied. To understand such relationship, this study has mainly three components namely 1) Reproduction of the 2011 tsunami, 2) Damage investigation and 3) Developing fragility functions. The source models of the 2011 tsunami were verified and adjusted so that the tsunami characteristics were able to accurately reproduce in the target area. Damage ratios of the aquaculture raft and eelgrass were investigated using satellite images taken before and after the 2011 tsunami through visual inspection and binarization. The tsunami fragility functions were then developed based on the relationship between the simulated maximum flow velocity and the calculated damage ratio. It was found that the damage ratio of higher than 0.5 is equal to the maximum flow velocity of 0.8 m/s (aquaculture raft) and 1.0 m/s (eelgrass). Whereas, the damage ratio of higher than 0.9 is equal to the maximum flow velocity of 1.3 m/s (aquaculture raft) and 3.0 m/s (eelgrass). It was found in this study that the tsunami amplitude had no relationship with the damage ratio. In addition, the proposed fragility functions for the aquaculture raft are getting along well with the previously proposed damage criteria. The proposed fragility curves will be useful for marine product and environmental damage assessment but also suggestion for the zoning of aquaculture raft to mitigate impact from tsunamis in the future.

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 A new type of tsunami risk map so that vessels evacuate to the safe area during tsunami warning was proposed. The method can evaluate risky sea area that was not considered by the conventional methods. Several tsunami simulations are conducted for several earthquakes, then the tsunami risk map is obtained by the combination of the maximum tsunami velocity map and the probability map that exceed the velocity to enable the steerage of vessels from the results of all tsunami events. We created the tsunami risk map of entire area of the Tokyo Bay using the proposed method, and found the higher-risk area: the port or harbor inner of the Tokyo Bay. The vessels that are anchored in the port of Yokosuka were verified if they move to the safety zone in an incoming tsunami, the result indicated that several types of vessel required the countermeasures to reduce tsunami damages.

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 Shizuoka Prefecture, located on the Pacific side of Japan, anticipates major influence due to the Nankai Trough Earthquake. To evaluate potential hazards and risks due to future devastating tsunamis, coastal defense structures in Shizuoka have been designed against L1 tsunamis (once in about 100 to 150 years) and L2 tsunamis (once in about 1,000 years). However, the current deterministic procedure of deciding upon L1 design tsunamis lacks rigorous consideration and discussion of uncertainties associated with possible tsunami sources. In this study, a new method of determining the design tsunami heights probabilistically, using stochastic tsunami models in the range of Mw 7.8 to Mw 9.0. The stochastic method consists of several calculation steps, i.e. stochastic slip generation, initial tsunami profile determination, and numerical simulation of tsunami propagation. The exceedance probability curves of tsunami heights along the coastline in Shizuoka were estimated and compared with the current estimates based on the L1 tsunami and the L2 tsunami which are published by Shizuoka Prefecture. The results indicate that the current L1 tsunami heights at some locations correspond to return period longer than 200 years (i.e. overrated). To define L1 tsunamis more objectively and consistently, the proposed probabilistic approach is suitable.

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 This research aims to reduce the tsunami misdetection in the observation data of GPS buoys and to increase the efficiency of tsunami detection. By using the index of Position Dilution of Precision, reliability of GPS satellite positioning and satellite number for calculation, it was possible to extract about 43% error waveforms without the reduction of the tsunami detection rate. In addition, the frequency characteristics of error waveform and tsunamis are clarified by using the continuous wavelet transform, and further error waveforms extraction become possible.

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 We attempted to observe the 2015 Illapel Earthquake Tsunami in Japan by using the oceanographic radar, however we could not detect it. Hence, we carried out numerical modeling of the tsunami and showed that the tsunami velocity was smaller than the observable velocity of the radar. On the other hand, a numerical experiment of the 1960 Chile Earthquake Tsunamis indicated that the radar could have detected it. Further, we conducted a virtual tsunami experiment including background noise and observation flow. The experiment result showed that the tsunami detection distance was 25.5 km when cross-correlation calculating period and distance were 3 hours and 3 km.

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 Using the Enks method, I also verified whether it can be predicted with sufficient accuracy even in the S-net observation network. As a result, it is clear that the tsunami real-time prediction can be performed with almost the same precision as in the case of DONET2 of the Nankai Trough when the observation time is 5 minutes. Moreover, I investigated the effect on accuracy of off-shore tsunami gauge configuration as S-net. As a result, it is firstly clear that the accuracy of the prediction at the point which the tsunami arrives will decrease if there are no observation points in the place where the tsunami propagates from the source. Secondly, it is clear that even if the observation point is placed only in the area where the gap of the earthquake fault is large, it can not be predicted with good accuracy in the coastal area. Conversely, even if there are no observation points near that area and if the tsunami propagated from that area is observed at the inland observation point, the prediction accuracy will not be worse.

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 To assess paleo-tsunami history, we studied coastal lowland on Nikaho city, southern part of Akita Prefecture, at the eastern margin of Japan Sea. From eight boring cores in these study area, we found two coarse grained sand sheets in fine sediments beneath the wetland. These sand sheets has some sedimentological characteristics of an event deposit, such as, erosional lower contact, rip-up crusts, parallel and cross stratifications, upward fining, and plant fragment laminae. These sedimentary features indicate formed by strong currents. We recognized these event deposits as a tsunami deposits based on their distribution pattern, sedimentary features and geographic setting around these boring sites. We used radiocarbon ages from plant materials to determine the ages of deposition of these tsunami deposits. Depositional ages of these tsunami deposits were interpreted the 12^th to 13^th -century and after the 14^th to 15^th -century by calibrated ages. These tsunami deposits extends about 110-190 m inland from the present shoreline.

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 Regional Oceanic Numerical simulations using ROMS with tidal forcing were conducted to investigate tidally induced internal waves (internal tides) in the vicinity of the Izu-chain Islands. The tides enhance the enrgy flux of internal waves by about 10 times as large around the islands. Therefore, in the study region, the internal waves are considerably enargized by the tidal forcing. Although the total and baroclinic components of kinetic eneygy increase due to the tides, the barotropic kinetic energy component decreased by the tidal forcing. The internal waves accompanied by strong baroclinic flows largely contribute to the flow compared to the currents due to winds and the Kuroshio. The numerical simulateons also revealed the enhanced eddy motiions due to the tidal forcing, suggesting that the tides contiribute to lateral mixing or transports via meso- and submesoscale eddies.

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 The Kuroshio off Japan is accompanied by vigorous eddy and frontal activity both on meso- and submesoscales, which significantly affects the biogeochemical productivity in the upper ocean. We examine the seasonal variability of eddy-induced nitrate transport and resultant biogeochemical response around the Kuroshio using a climatological ROMS-NPZD model. A nitrogen budget analysis indicates that nitrogen exists mostly in the phyto- and zooplankton compartments in both the Kuroshio and Kuroshio Extension regions during the sping bloom. The increased zooplankton further enriches detritus that settles down by about 100 m, leading to an increase of ammonium below the mixed layer. In winter, eddy-induced nitrate transport is enhanced in the region about 1° away from the Kuroshio axis. The baroclinic instability due to the surface cooling in winter generates meso- and submesoscale eddies and substantially promotes eddy-induced vertical nitrate transport.

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 Three-dimensional inclined thermals are analyzed using Dynamic SGS model. The analysis model consists Finite Volume Method (FVM), TVD-superbee scheme. The variations of the travel speed, the maximum width and the maximum height of the three-dimensional thermals are obtained from numerical results and compared with the experimental results. The agreement of numerical results and experimental ones is fairly well and it is found that this model can reproduce behavior of three-dimensional thermals on inclined wall.

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 As part of restoration of the breakwater at the entrance of Ofunato Bay, which was damaged by the 2011 Tohoku Earthquake Tsunami, flow pipes with a diameter of 3.5m were placed through the bottom of the breakwater to enhance water exchange between the inner and outer bay. The aim of this research is to understand the effect of these pipes on the occurrence of low oxygen water based on field experiments conducted after the completion of the breakwater. These field experiments indicate that the main effect on water exchange due to the flow pipes was the discharge of low temperature, high density water masses inside the breakwater to the outside of the breakwater, with flow speeds in the pipes sufficient to discharge the entire volume below the top mound of the breakwater (-16 m depth) in about 10 days. The effect of this enhanced exchange was to allow easy intrusion of low temperature water masses that appeared in the outer bay into the lower layer of inner bay. Since the temperature inside the mounds had been increasing, the cold water intrusion prevented the inner part of bay developing a persistent low oxygen environment.

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 Recently, various coastal conservation measures based on comprehensive sediment control have been conducted, there are however many unkown phenomena in sediment transport and deposition around river mouth under flood condition. In this study, a series of hydraulic model experiments on turbidity current were carried out in order to grasp the behavior and deposition characteristics of the turbidity current. We applied the theoretical formula proposed by Hirano and Hatano to both salinity and turbidity currents. Experimental results showed that factors influencing turbidity current behavior include (1) resistance by scattering of fine particles, (2) density change due to sediment deposition, (3) tip velocity at the depth where most coarse particles deposit. The theoretical formula showed good agreement in tip velocity with both the salinity current and the turbidity current considering decrease in density by deposition.

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 River water temperature shows upward trend due to climate change. However, its effects on thermal stratification in a coastal area is not clear. We tried long-term field measurement of river water temperature at river discharge stations in A-class rivers in the Ariake Sea, and numerical simulation of stratification in the bay using the measured hourly river water temperature dataset. As a result of this research, the followings are clarified: 1) river water temperature at the lowest station of the river has high correlation with air temperature; and 2) river water temperature has a significant effect on thermal structure in the bay during a flood event. Possibility of enhancement of stratification in the bay due to global warming was indicated.

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 Since explosively developed extratropical cyclones often cause severe damages to coastal area around the Japan Sea in winter, the long-term assessment of winter extratropical cyclones is required for engineering purpose. However, extratropical cyclones around Japan have not been understood well about intensity, frequency and etc. An algorithm of extracting extratropical cyclones from the atmospheric data of JRA-55 was developed and the extratropical cyclones have been analyzed from the viewpoints of correlation with teleconnection patterns and cluster analysis of tracking data.

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 On 30 August 2016, Typhoon Lionrock (2016) moving northwestward made a landfall at the Pacific side of the Tohoku district, Japan, in which there were no records of typhoon landfalls since statistics started in 1951. In order to investigate the mechanisms of Lionrock taking unique pathway, the stearing currents induced by each of potential vorticity (PV) anomalies surrounding Lionrock were estimated by an analysis of the piecewise PV inversion in this study. At 1200UTC 30 August 2016 when Liorock just made landfall around Ofunato City, Iwate, Japan, the analysis suggested that Lionrock moved northwestward by the southeasterly wind with a wind speed of about 20 m/s, which was induced by three different surrounding PV anomalies: 1) an upper-level dry positive PV anomaly originating from an upper cold low, 2) a low-level wet positive PV anomaly developed by cumulus convections under the upper cold low, and 3) an upper-level wet negative PV anomaly intensified by cumulus convections.

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 Urbanized coastal low-lying area has vulnerability against flood and inundation, which are caused by multiple flood causing factors occurring in coast, river and urbanized areas. Integrated flood prediction model, “Seamless Model”, has been developed to simulate inundation caused by tsunami, storm surge, as well as river flood and urban inundation. This study applied the model to realtime inundation forcast simulation based on high-resolution precipitation nowcast data. Simulation test to past typhoon event indicated that this method can accurately predict forth-coming inundation in several tens of minutes. Field observation was also conducted to collect the water level data of sewerage pipes to validate the model.

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 In Nagoya Port, large ships navigating in the main channel generate significant ship waves, which cause unexpected ship motions of berthing ships. Rollover accident of a small ship due to ship waves happened in the past, so that safety measures against the ship waves have been investigated.
 In this study, findings contributing to future safety measures are summarized according to field observation data on wave agitation in the channel and numerical simulation on ship waves. Ship waves affectted by natural conditions in the navigation channel are summarized, as well.
 As a result, the relationship between wave heights of ship waves and ship speed is identified, in which ship waves depend predominantly on the ship type and the navigation condition of entering and outgoing the port. By applying the relationship, estimated formulas on wave height of each ship conditions are proposed. In the course of the study, it is confirmed that the propagating ship waves are affected by tide level and bathymetry, which create remarkably amplified point of wave height appearing in different area. The constant direction current due to Kiso River out flow is confirmed to affect also ship waves, in which ship waves generated by entering and outgoing ships are different in wave height.

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 Investigation of sand ripple forming process on a seabed of inshore area is indispensable to understand the structure of the boundary layer. In addition, the shape of the sand ripple is of significant concern as the roughness of the seabed when the coastal morphodynamics is discussed. However the mechanism of the ripple formation is still not fully revealed. This will be due to the quite difficulty in implementation of measurement or simulation under complex boundary condition by the wave breaking. In this study, the ripple formation process is reproduced by coupling of enhanced MPS method, which is superior to simulate violent free surface flow, and DEM method, which has a distinct advantage of tracking movable bed. Furthermore, the ripple formation process is discussed in terms of the effect of pore flow.

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 The object of this study is to clarified the mechanism of scouring in sandy ground due to the tractive force and seepage force. Especially, in this paper, are discussed to generating of excess pore water pressure induced by free surface flow using the movable bed experiment and CFD-DEM simulation which is considered by the interaction between soil particle and fluid. As a result, seepage flow in the ground surface was generated by free surface flow and the excess pore water pressure was induced by the difference in velocities around the surface and the shear deformation in fluid layer with 4 times thickness of mean particle diameter closed to the surface of ground.

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 This study focuses on behavior of coral gravels under forward leaning waves around the surf and swash zones. We first carried out laboratory experiments in which waves and moving gravels were captured through the analysis of video images recorded from the side of the flume. It was found through comparisons of these time-varying quantities of water surface fluctuations and velocities of moving gravels and surrounding currents that the acceleration of near-bottom fluid and associated bed slopes appear to have significant influence on movement of coral gravels.

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 The present study was used a high-speed camera to analyze the movement of the ground surface layer due to a horizontal flow. In this study, the movement characteristics of soil particles due to flow was evaluated using particle image velocimetry (PIV) analysis and examined the change in the pore water pressure in the ground. At the initial stage of the experiment about 16s, the overturning, sliding, and saltation of soil particles were observed in the surface layer. At this time, the excess pore water pressure ratio was approximately 0.36. From after the 30s, the excess pore water pressure ratio to 3.0 mm depth was 0.8 or higher. At 86.5 s after the start of the experiment, soil particles lying between the ground surface and 1.825 mm depth (11 particles) were moved for the vertical direction. Subsequently, the soil particles was moved toward the downstream side due to the horizontal flow. Therefore, the results have shown that the soil particle motion due to a flow was affected by the tractive force and the change in the pore water pressure.

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 The critical tractive force of a cohesionless material, which is subjected to upward seepage flow, is investigated. For example, when a river bed is subjected to the upward seepage flow and the seepage water is injected into the river flow, the upward seepage force exerted onto the sand particels of the bed decrease the virtual weight of the sand, which may also reduce the critical tractive force determining the incipient motion of the particles. A test apparatus has been built and the effects of the injection on the critical tractive force of glass beads have been measured: a pipe with a rectangular cross section was used for the water channel and a section of a movable bed subjected to the upward seepage flow was installed to the bottom of the channel. The test results have shown that the critical tractive force of the cohesionless material slightly decreases as the hydraulic gradient of the seepage flow increases. However, it does not drastically decrease even when the hydraulic gradient reaches the quick-sand condition.

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 The characteristics of sediment transport according to saturation of the sand slope under mixed grain size are investigated experimentally and numerically. The movement of fluorescent sands with different colors for each grain size are measured in solitary wave experiments. As the result, in the case of saturated condition, the sediment transport becomes larger constantly due to uplift force of the seepage flow. In particular, increasing of the fine sand components is significantly. This phenomenon leads to coarse granulation of bottom sediment and steepening of the foreshore gradient accelerates even further. A numerical approach of tractive force for respective grain sizes of sand mixtures is presented, that is quantified through a permeable Shields parameter. The results of prediction are in good qualitative agreement with those of experiments.

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 Field observation at offshore area of inter tidal flat around the Kumamoto Port in the Ariake Bay and flume experiments were carried out in order to elucidate sand-mud mixture sediment dynamics due to waves and tidal currents. Through the field observation, the mud content is found to be an important factor that controls the sediment transport rate. Bedload transport rate under waves and tidal currents were measured through a flume experiment using several sand mud mixture samples with different mud content. Numerical model that incorporate the sand mud mixture process were also set up and simulated results were validated with the flume experiment data. The study finally clarified some problems in reproducibility of sand-mud mixture dynamics as future works.

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 This research is to design the coastal structures in Kochi Coast where cross-shore sediment transportation is dominant. Cross-shore sediment transportation induced by high waves and current flows near structures was studied by hydraulic model experiments. Then a numerical model that evaluates cross-shore and alongshore sand transportation was developed.
 Using this model, shore structures' effect as beach protection was evaluated. Artificial Headlands were proposed as the optimum design of the coastal structures. Furthermore, the optimum size and shape of the headlands was proposed by evaluating the beach protection and the flows analysis near structures using the hydraulic and numerical models.

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 The numerical model for topographical change of a ship channel mainly due to siltation in stormy waves has been improved by taking into account observed and surveyed data of marine and topographical conditions in two different typhoons. The results simulated by the model have showed that the tidal phase at the highest wave affects the topographical change in a ship channel. The affection of the tidal phase like flood or ebb is comparatively small for the case of long duration of high waves, but it becomes large for the case of their short duration. These results suggest that the tidal phase at the highest waves is important as well as the duration of the stormy waves for the prediction of siltation in a ship channel.

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 In this study, We inspected whether the multiple longshore bar is formed by the combination of three kinds of different erosion type waves of the breaking position experimentally. When the wave acted in low order of the wave height, the bar which was formed of a low wave of the wave height was disappeared by the action of a high wave of the wave height, and became the equilibrium beach section which existing only the bar which was formed of the high wave of the wave height. In contrast, when the wave acted in high order of the wave height, the traction excelled in the offing side of the breaking position, and the bar which was formed of the high wave of the wave height was disappeared by the action of the wave which was lower than it. Therefore, in the experiment using the rule wave in beach incline 1/15, when it acted by the different erosion type wave of the breaking position, the equilibrium beach section of one step of the bar was formed by the wave which acted finally. From this, it is thought that it is difficult for the multiple longshore bar to form it by the combination of waves under this experiment condition.

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 Filtration flow has an important role in the function of a set-back type floodway, and it depends on the composition of beach material of the berm. In this study, field experiment on the drainage from the floodway was carried out, while considering the improvement of ordinary-type Numakawa-daini floodway into the set-back type. Then, two-dimensional movable experiment was carried out to investigate the filtration flow in the sand layer. In the berm composed of sand and gravel, the intensity of the filtration flow increases with the water level behind the berm, and fine sand is transported away by filtration flow, resulting in increase in the intensity of filtration flow.

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 Beach profile change in the foreshore zone was affected by wave-induced cross-shore sediment transport. Until now, the characteristics of cross-shore sediment transport in the swash zone at the Hasaki coast, Japan have been investigated, and a foreshore beach profile change model was proposed. The model was applied to the Hasaki coast, and it is reported that the shoreline change and the ground elevation change were reproduced with enough accuracy. In order to apply this model to different coasts, however, it needs to include the effect of beach slope on the wave characteristics. In the present study, the model was modified that the unknown parameters were used in the estimate equation of the maximum wave runup height, and the modified model was applied to the different coast with steep beach slope, i.e. coarse sediment diameter. The results were verified with observed field data and found that the model can correctly reproduce the ground elevation and shoreline changes. Thus it is suggested that the model could be used for different coasts by using parameters related to the sediment diameter of the coasts.

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 On a sand dune, a blowout is often formed owing to wind effect. The formation of a blowout was observed on November 25, 2016 at the Node coast facing the Pacific Ocean, where a blowout has been formed to leave a concave topography. Then, a model for predicting the formation of a blowout was developed using a cellular automaton method, in which two important factors of saltation and avalanche were considered. The results of the numerical simulation were compared with the measured results on the Node coast, and the predicted and measured shapes of the blowout were in good agreement.

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 Numerical simulations of sediment transport, which was caused by the 2011 Tohoku Tsunami, were conducted in order to investigate the influence of computational parameters on accuracy of movable bed model for tsunamis. Simulation results revealed that the amount of sediment transport differed depending on saturation concentration of suspended sediment. Erosion volume was underestimated in the case that saturation concentration was given as a constant value (1%). On the other hand, erosion caused by the strong return flow was reproduced using saturation concentration of suspended sediment which varies depending on the flow fields. The simulation results also showed that the sediment transport coefficients in the governing equations had relatively less effect on the sediment transport.

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 Coastal dune and its vegetation have potential to reduce tsunami damage in the hinterland. However, no studies have mentioned the conditions to produce their effect against tsunami. Numerical experiments on sediment transport and tsunami inundation in consideration of tsunami absorbing effect and erosion resistance effect of the coastal vegetation were performed for a cross-section in Natori City, Miyagi Prefecture. The height of the narrower coastal dune decreased more than that of the other coastal dune profiles. The erosion at the landward slope saliently varied according to the vegetation conditions. These results showed the width of coastal dune was important to produce their effect against the tsunami, and that the management of the vegetation was important when the width of the coastal dune was not enough against the tsunami.

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